Conventionally, hydraulic or pneumatic actuators are used, although other types of actuator, e.g. electrical or mechanical, may also be used. The actuators generally comprise an extendible rod or arm that is attached to open the cowl as it extends and close the cowl as it retracts under the weight of the cowl door.
A typical hydraulic actuator comprises a piston rod, a cylinder and a rotatable lock mechanism to facilitate mechanical operation of the cowl door or flap. Pressure is applied to fully extend the actuator; when fully extended, pressure is removed allowing the actuator to retract by a small amount which causes the actuator to lock, as the lock mechanism rotates and engages the actuator. To close, or stow, the cowl door, the actuator is then extended by application of pressure out of the locked position to its fully extended position from which, as pressure is removed, the actuator is able to return to a retracted, stowed, position.
A rotatable lock mechanism, in cooperation with a lock pin, provides the paths for the actuator to take up its locked position or return to its stowed position, as will be described further below.
Whilst such an arrangement permits locking of the actuator in an extended position, and so does not require the associated hydraulic pump to be operating throughout the period of time that the associated door or doors are to be held in their open positions, there is a risk that if the actuator has not fully extended before being retracted by a small amount to take up the locked state, the actuator may come to rest in an intermediate position and appear to be locked in its extended position without the locking mechanism being properly engaged. In such circumstances, after the hydraulic pressure has been removed, jarring or vibrations could result in disengagement of the lock arrangement and the actuator being unable to hold the door(s) in the open position. Clearly, this is undesirable.
EP 2532821 describes an improved actuator mechanism that avoids the actuator stopping in such an intermediate position. EP 2532821 provides a resilient detent in the paths for a locking pin provided by the lock mechanism such that once the locking pin has moved beyond a predetermined position in the extending direction the resilient detent prevents return movement of the pin along the entry path.
A further problem has been identified with the known actuator mechanism when the actuator is used to return the cowl to the stowed state. Here, as mentioned above, the actuator is extended (out of the locked state) and then, due to the paths defined by the lock mechanism, returns to the retracted state, via an exit path. If, however, the actuator is not fully or sufficiently extended to clear the path for the locked state, the pin can again become stuck in position at an intermediate point, rather than automatically feed into and follow the exit path under the weight of the cowl. This intermediate position can be falsely interpreted as a locked state. If the actuator is jolted or slightly disturbed, the locking pin can slip from the intermediate point, back into the locked position, which can damage the door as well as damage other parts or cause injury.
Systems such as described in EP '821 include a feature that prevents this problem to some extent. A spring biased detent ball retainer (described further below) ensures that before the actuator locks onto such an intermediate point, the detent ball which is timed to run over a cam-like profile, rotates the collar lock so that the lock pin either moves into the locked state or the unlocked state.
Reliance of the lock mechanism on the torque generated by the spring biased detent ball, however, limits the degrees of angular deviation at which the actuator can operate. Torque generated by the spring biased detent ball shall always be greater than the varying resistive torque. The torque generated is highly sensitive to the cam-like profile that the detent ball traces. The resistive torque depends upon factors such as thickness of the thin fluid film between the piston and lock collar (clearance), viscous drag on surfaces of rotating components, viscosity of working fluid which is, in turn, a function of ambient temperature.
The present disclosure therefore aims to provide an actuator locking mechanism that can prevent the actuator becoming stuck in an intermediate position when intended to be moved from the locked position to the stowed position, without reliance on a spring biased detent ball.
The present disclosure provides an actuator system comprising a rotatable lock mechanism defining a path for an actuator pin as the actuator is expanded and retracted, wherein the lock mechanism defines an entry passage through which the pin enters as the actuator extends, a guide surface along which the pin travels from the entry passage as the actuator retracts, a locking recess into which the pin is guided by the guide surface, and an exit passage into which the pin is guided as it is caused to leave the lock recess by extension of the actuator and subsequent retraction; whereby a detent surface is provided to prevent the pin returning back into the lock recess when the actuator is extended to cause the pin to leave the lock recess, wherein the lock mechanism comprises a collar defining the path and a tine gate fitted within the collar and comprising a detent finger defining the detent.
In some embodiments, the guide surface and/or the detent surface provide a slope.
A detent surface may also be provided in the entry passage.
The lock mechanism of the second aspect may provide advantages alone or in combination with the detent of the first aspect.
The rotatable lock mechanism comprises an interlocking collar and gate ring combination whereby the detents are provided on a gate ring that is nested under the collar.
A spring biased detent ball arrangement may be provided across the inner surface of the lock mechanism.
Preferred embodiments of the invention will now be described by way of example only, and with reference to the drawings.